1. Field of the Invention
The present invention relates to lens fabrication of continuous stratified indices of refraction at short wavelengths and more particularly to lens fabrication in the IR, visible and ultraviolet wavelength regimes.
2. Description of the Related Art
Among the enabling technologies that are desired by the contemporary aerospace art are sensors that are capable of detecting, and/or discriminating types of targets, and even identifying actual targets beyond the radar regime. This would enable one to diminish the effectiveness of stealth design. Further, it is desired to have the capability of a wide field of view to allow for a lighter, lower volume system than now exists. It is also desired that a sensor be geometrically adaptable to the carrier vehicle's geometry so as to minimize the sensor's contributions to aero-drag and radar backscatter. The sensor should be capable of operation somewhere in the IR through the near UV spectral regimes, so a stealth design of the target is not readily feasible. The technology must possess a very wide field of view and an appropriate angular resolution accuracy to be able to detect targets at tactically interesting ranges and be capable of operation somewhere in the IR through the near UV spectral regimes.
Stratified lenses are found in living species, from insects to human beings, to provide wide-angle vision. Such vision, for example, provides increased awareness of predators.
During World War II, R. K. Luneberg performed fundamental geometric optics investigations on stratified lenses. The desire was to maximize the field of view by continuously changing the index of refraction with position. In particular, he proposed a spherical lens with a particular stratified distribution that produced a maximum field of view of 2.pi. steradians.
U.S. Pat. No. 4,288,337, issued to H. Ota et al., describes a method to lower the weight of an artificial dielectric by using fewer loadings of high dielectric constant. However, Ota's loadings are not sub-micron, as are necessary for use in very short wavelength regimes. Ota's loadings are of millimeter size applicable solely to the radar field of many centimeter wavelength. His loadings are metallic coated which at short wavelengths would block the waves from being influenced by their dielectric values and result in a very lossy system.
U.S. Pat. No. 5,421,848, issued to G. Maier et al., similarly describes a lens for the microwave domain. As in the Ota et al. patent, Maier et al. did not teach how to extend the technology to the IR, visible, and UV regimes.
U.S. Pat. No. 2,849,713, issued to G. P. Robinson, Jr., also describes a microwave system without teaching how to extend the Luneberg art to the shorter wavelength regimes.
U.S. Pat. No. 3,666,347, issued to 1. Kitano et al., describes a lens of millimeter size loadings appropriate to microwave wavelengths, without teaching how to extend this technique.
U.S. Pat. No. 3,914,769, issued to W. J. Andrews, describes another method suitable only in the microwave regime.
Other patents that pursue the Luneberg lens concept include the following: U.S. Pat. No. 5,047,776; U.S. Pat. No. 5,638,214; U.S. Pat. No. 4,025,157; U.S. Pat. No. 4,830,454; U.S. Pat. No. 5,225,668; U.S. Pat. No. 5,384,458; U.S. Pat. No. 3,307,187; U.S. Pat. No. 2,761,141 and U.S. Pat. No. 4,531,129.
None of these aforementioned patents describe the application method disclosed in the present patent application.